For certain light sources, such as LED or Fluorescent sources, the peak brightness is fixed and cannot be modulated. Manufacturers of light sources with fixed brightness dim the brightness of the light source by shortening the duty cycle. The duty cycle of the light source is kept on for a part of the cycle, and off for the rest of the cycle. A typical LED cycle frequency is in the 300-700 Hz range. However, there is no standardized LED cycle frequency.
In current electronic display applications there may be a problem with flickering when displaying images of light sources. LED light sources are pulsed to turn on and off many times per second. Specifically, flickering happens when there is a camera exposure that is shorter than a LED cycle length (i.e., when using multiple-exposure High-Dynamic-Range (HDR) to capture a high dynamic range scene or when using short exposure to capture ultra-bright conditions). Furthermore, there is no current industry standard for the frequency or duty cycle of pulsing for LEDs. Therefore, designing an electronic display capable of handling a specific frequency or duty cycle is impractical.
It would be desirable to implement a reduction of LED headlight flickering in electronic mirror applications.